1. Field of the Invention
The present invention relates generally to a lighting system for providing a uniform light distribution, and particularly to a cylindrical lens for uniformly lighting long shelves in a refrigerator compartment
2. Description of the Related Art
A prominent means of lighting long store-shelves is the fluorescent lamp, due to its low cost and good luminous efficacy. While the linear geometry of this lamp is appropriate for long shelves, its isotropic radiation pattern is not, because most of the light misses the target, unless bulky and expensive reflectors are employed. Also, the light that does make it to the shelf is not at all uniform.
In addition, lighting cold storage compartments, such as commercial refrigerators, provides unique issues. The lighting equipment produces heat yet the hot lights are operating within a cold environment. This cold hinders the performance of the fluorescent lights. In particular, in such cold compartments, fluorescent lamps are disadvantageous due to their energy efficiency and their reduced lifetime of only a few thousand hours. Additionally, the lighting should be adequate to illuminate the products within the compartment and should be visually appealing to catch the eye of the consumer.
Light emitting diodes, however, have greater efficacy and even longer operational life (e.g., 50-100 thousand hours) at low temperature in comparison to fluorescent tubes which also produce the highly nonuniform illumination. The major advantages longer life, lower power consumption, as well as compact package size make LEDs a desirable light source for illuminating supermarket freezers.
Low-cost LEDs can be economically provided on low-voltage tapes, spaced every 10-20 mm, such as those sold by the Osram GmbH, Munich, Germany, under the ‘Linear Flex’ product line. Furthermore, because LEDs radiate into a hemisphere (or less), optical lensing can be employed to distribute their light output. Typically, such optics have been mounted individually on the LEDs as domes. Such conventional dome lens, however, do not produce the desired illumination, e.g., substantially uniform, in this setting where, for example, the objects, are close to the LEDs but are also wide.
What is needed is optics for providing uniform illumination for products on a shelf in a commercial refrigerator where the shelf is inches from the LEDs yet is wide, e.g., at least 2 feet. The present invention will remedy the current lack of suitable optics for uniform-illuminance LED shelf-lights, and in particular will provide numerous preferred embodiments for different illumination geometries for use in commercial refrigeration.